The sulphate and its reduction products could be accumulated in Dual Coupling of Ethanol and Methane Fermentation Process which do harm to the whole process.The effect of three sulfides including sulphate sulfite and sulfion on ethanol fermentation of very high gravity cassava mashes(the ratio of cassava and water to 1∶ 2.2(w/w) was researched in this article.The final results showed that sulfite and sulfion had great influence on ethanol fermentation,but sulphate had not.With the sulfite and sulfion concentration increased under the experiments concentration,the yield of ethanol decreased and the byprocuct glycerol increased.The lag phase delayed when the fermentation mashes added with sulfion.It delayed to 48h when the sulfion concentration was 6.0 mmol/L.Both of the two sulfides that harmed ethanol fermentation needed to be eliminated during the dual coupling fermentation.